1. Field of the Invention
The present invention relates to the protection of electronic chips, particularly in the case of their use at microwave frequencies.
2. Discussion of the Background
It is known to produce electronic cards comprising a support or base, a connection plug and at least one chip with its connection circuits. The support is a plane plate, generally made of brass, on which the chip and a printed-circuit part which includes the connection circuits for the chip are placed; this printed-circuit part is connected to the chip by wire bonds.
In order to mechanically protect a chip mounted in this way in an electronic card, it is known to encapsulate it in a product such as a resin. To do this, resin is deposited on the chip and its wire bonds to the connection circuits; after the resin has cured, it forms a kind of shell which effectively protects the chip and its wire bonds.
However, these chips are designed to operate with radiofrequency propagation in a heterogeneous medium which is, for example, air and GaAs; now, the resin transforms this medium into an air/resin/GaAs medium and as a result the propagation, and therefore the electrical behaviour of the chip, are modified. This modification is all the less acceptable the higher the operating frequencies and, in practice, the encapsulation process indicated above allows operation only at frequencies of less than 10 GHz.
The object of the present invention is to propose an encapsulation process which allows operation possibly up to 50 GHz.
This is achieved by controlling the amount of resin deposited so as to reduce the thickness of the latter to a thin layer and therefore to reduce, consequently, the perturbating effects.
According to the invention, what is proposed is a process for encapsulating an electronic chip in the case in which, on the one hand, this chip is placed on a mechanical support having a plane face and in which, on the other hand, part of a printed circuit having a thickness greater than the thickness of the chip is also placed on the support and. at least partially surrounds the chip, characterized in that it consists in providing a tab in the support, which projects from the plane surface, in raising the chip by placing it on this tab, in choosing a tab thickness such that, with respect to the plane face, the height of the top of the printed-circuit part is greater than the height of the top of the chip and that the difference between these two heights is less than a predetermined value, in filling the space between the printed-circuit part and the chip with an encapsulation product as far as the upper level of the printed-circuit part and in curing the encapsulation product.
According to the invention, what is also proposed is an electronic card which includes at least one electronic chip, characterized in that the chip is protected by encapsulation carried out according to an encapsulation process described in the above paragraph.